A 3D framework for geological media with multiple intersected fractures : coupled Darcy flow and Fickian diffusion

Abstract

Despite extensive research on computational geomechanics and fluid dynamics, accurately simulating convection-diffusion (CD) processes in complex fractured systems remains a significant challenge. This study develops a 3D numerical framework for modelling CD processes in fractured geological media. The framework integrates Darcy's law and Fick's law, considering flux interactions between the matrix and fractures. The meshing strategy generates high-quality grids even in scenarios involving intersecting fractures. Then, a unified numerical scheme for solving the CD system is proposed. The novelties of this work include: (1) The proposed framework enables effective simulation of 3D fractured media, including more complex fractured vuggy media; (2) The numerical method precisely discretizes the CD terms in governing equations; (3) A Non-Orthogonal Correction (NOC) method, combined with an adaptive time integration scheme, is proposed for eliminating errors induced by skewed grids; and (4) The effects of fracture patterns and heterogeneity on flow are thoroughly analysed. The proposed method is validated through benchmark tests, demonstrating the superiority of the NOC method compared to classical methods. Further analysis reveals the evolution characteristics of pressure and concentration, offering insights into the effects of fracture patterns and heterogeneity on flow and diffusion processes.